Tubulovesicular structures--the ultrastructural hallmark for transmissible spongiform encephalopathies or prion...

Tubulovesicular structures (particles--TVS) are the only ultrastructural marker for all transmissible spongiform encephalopathies (TSEs) or prion disease as seen by thin section electron microscopy. The latter is stressed as opposed to negative-staining techniques. TVS are spheres or short rods of approximately 27-35 nm in diameter. What is particularly interesting, this size of TVS is also the size of filter cut-off as judged from ultrafiltration studies and the size of the smallest infectious unit as recently estaimated. TVS have been found in all naturally occurring and experimentally induced TSEs, including variant Creutzfeldt-Jakob disease and human familial TSEs--fatal familial insomnia and Gerstmann-Sträussler-Scheinker disease. In longitudinal studies, the number of neuronal processes containing TVS correlates roughly with the incubation period and with infectivity. Hence, they are readily found in hamsters infected with the 263K strain of scrapie but it is very difficult to find them in human TSEs where titre is lower. The composition of TVS is unknown but they are not composed of PrP. Their consistent presence in all TSEs suggests the role at least of TSE pathogenesis.